The present invention relates to a wellbore system including a main wellbore extending from surface into the earth formation and a plurality of branch wellbores. Such wellbore system is generally referred to as a multilateral, or branched, wellbore system.
In applications where hydrocarbon gas can be simultaneously produced via the branch wellbores so as to form a commingled stream of gas in the main wellbore, it is desirable to provide a system enabling the identification of those branch wellbores which are producing hydrocarbon gas.
Furthermore, in case one or more of the branch wellbores is producing at an undesirably high flow rate, it is desired to provide a system and a method which allows identification of said one or more of the branch wellbores.
Accordingly it is an object of the invention to provide a system and a method for determining which branch wellbore of a multilateral wellbore system is producing hydrocarbon gas.
In accordance with the invention there is provided a system for identifying a producing branch wellbore of a multilateral wellbore system including a main wellbore extending from surface into the earth formation and a plurality of branch wellbores, each branch wellbore being provided with a conduit for passage of a stream of hydrocarbon gas from the earth formation to the main wellbore, the system comprising a plurality of sound generating devices, each sound generating device being arranged in a corresponding one of said conduits and being operable to produce a sound wave of selected frequency upon flow of the stream of gas along the sound generating device, the frequencies of the sound waves produced by the different sound generating devices being mutually different, the system further comprising a sound receiver capable of receiving each sound wave of selected frequency.
By operating the sound receiver a record can be made of the sound waves produced by the different sound generating devices. Since the frequencies of the sound waves can be linked to the respective branch wellbores, it can thus be determined which branch wellbore is producing hydrocarbon gas.
Preferably the sound generating device is operable to produce a sound wave of amplitude depending on the flow rate of the stream of hydrocarbon gas.
More preferably the amplitude of the sound wave increases with increasing flow rate of the stream of hydrocarbon gas. In this manner it is possible to determine the individual flow rates of the stream(s) flowing through the branch wellbore(s).
The method according to the invention comprises:
a) producing a stream of hydrocarbon gas flowing through a selected one of the branch wellbores to the main wellbore while the other branch wellbores are closed for hydrocarbon gas production;
b) inducing the sound receiver to create a calibration record of the sound wave produced by the sound generating device as a function of the flow rate of the stream of hydrocarbon gas flowing through the selected branch wellbore; and
c) repeating steps a) and b) for each branch wellbore. Preferably the method further comprises
d) simultaneously producing a plurality of streams of hydrocarbon gas flowing through the respective branch wellbores to the main wellbore;
e) inducing the sound receiver to create a production record of the sound waves produced by the sound generating devices as a result of the streams flowing through the branch wellbores;
f) comparing the production record with the calibration records to determine which branch wellbore is producing hydrocarbon gas.